This invention relates to a flow and pressure control valve system particularly designed for use with a two-speed transmission used in transport refrigeration units.
U.S. patent application Ser. No. 06/741,092 filed June 4, 1985 (W.E. 52,541) discloses a two-speed transmission used with transport refrigeration units which functions to permit driving a refrigerant evaporator fan at a higher speed than the refrigerant condenser fan. In that application, and as shown in a schematic embodiment of FIG. 4 of that application, a three-way valve under the control of a solenoid controls the output of a fluid pump in accordance with the particular position of the valve. The arrangement shown also requires the use of a separate pressure regulator in the system.
It is the aim of my invention to provide a flow and pressure control valve system in which a single valve of the design according to the invention performs various functions in conjunction with a separate two-way control valve. These functions include directing high-pressure fluid when required to a device such as a piston in a cylinder for shifting the transmission speed, controlling the system pressure within predetermined limits, and rapidly relieving pressure from the device when the pressure is no longer required, such rapid release of pressure being important in some applications. Additionally, the flow and pressure control system of the invention is less expensive and more reliable since the control valve is of relatively simple construction and easily manufactured, and the control valve, along with a separate two-way valve, replaces a three-way solenoid valve and a separate pressure regulator, the control valve itself having no more parts than a conventional pressure regulator.